MP Mark Lancaster has been criticised in a joint letter from all four candidates standing against him for election in Milton Keynes North.
The Labour, Lib Dem, UKIP and Green candidates have written a joint letter to the Citizen, promising not to take second jobs if they are elected in May.
And they criticise the current MP for his former second job for a venture capital firm, which netted him nearly £32,000 for 209 hours work - an hourly rate of £150 per hour.
The letter says: “We are united in our belief that the public want and deserve full-time commitment from whoever wins this forthcoming election. We have each committed that should we be elected we will not take any paid directorships or consultancies during our term of office.
“In addition, we would vote for legislation banning MPs holding directorships and consultancies and for a limit on what an MP can earn beyond his or her parliamentary salary.”
It was signed by Labour’s Emily Darlington, Lib Dem Paul Graham, Jennifer Marklew from the Green Party, and UKIP candidate Stuart Moore.
Ms Darlington stressed that the group were not criticising the Conservative MP for his time in the Territorial Army.
She said: “Mark Lancaster earned three times more in this parliament from paid consultancy for a property capital firm than with the army reserve.
“He has failed to explain how his work with Palmer Capital benefitted his constituents and whether he would take another paid consultancy if re-elected.
“I think voters have a right to know.”
Mr Lancaster said: “I am delighted to support a review to ensure that MPs cannot profit from a second job simply because they are an MP, but greater clarity is needed to ensure that some second jobs, such as service in the Army Reserve are not excluded either directly or indirectly through a salary cap, as I believe there is a wide consensus that such roles add value to Parliament, not detract from it.”